Check if you need to do a sequential test

Before you start a flood risk assessment, check if you need to carry out a sequential test. A sequential test compares your proposed site with other available sites to show which one has the lowest flood risk.

What to include in your assessment

For all developments covered by standing advice, you must put together a flood risk assessment which includes:

your site address

a description of your development

an assessment of the flood risk for your development (consider all sources of flooding not just rivers and the sea and include an allowance for climate change

the estimated flood level for your development, ie the 1 in 100 year river flood level or the 1 in 200 year tidal flood level

details of your flood resilience and resistance plans

any supporting plans and drawings

any information the relevant standing advice tells you to include

You may be able to get the estimated flood level from the Environment Agency or your local planning authority. If not, you’ll need a flood risk specialist to calculate this for you.

Your written flood risk assessment can be in any format, but must include the relevant plans, surveys and assessments. Check with your local planning authority if they have any specific software requirements, eg for producing detailed hydraulic models.

Minor extensions standing advice

You need to provide a plan showing the finished floor levels and the estimated flood levels.

Make sure that floor levels are either no lower than existing floor levels or 300 millimetres (mm) above the estimated flood level. If your floor levels aren’t going to be 300mm above existing flood levels, you need to check with your local planning authority if you also need to take
flood resistance and resilience measures.

State in your assessment all levels in relation to Ordnance Datum (the height above average sea level). You may be able to get this information from the Ordnance Survey. If not, you’ll need to get a land survey carried out by a qualified surveyor.

Your plans need to show how you’ve made efforts to ensure the development won’t be flooded by surface water runoff, eg. by diverting surface water away from the property or by using flood gates.

If your minor extension is in an area with increased flood risk as a result of multiple minor extensions in the area, you need to include an assessment of the off-site flood risk. Check with your local planning authority if this applies to your development.

You need to get planning permission to use a material that can’t absorb water (eg impermeable concrete) in a front garden larger than 5 square metres.

Access and evacuation

You need to provide details of your emergency escape plans for any parts of a building that are below the estimated flood level.

Make sure that your plans show:

single storey buildings or ground floors that don’t have access to higher floors can access a space above the estimated flood level, eg higher ground nearby

basement rooms have clear internal access to an upper level, eg a staircase

occupants can leave the building if there’s a flood and there’s enough time for them to leave after flood warnings

Floor levels

You need to provide both the:

average ground level of your building

finished floor level of the lowest habitable room in your building

Ground floor levels should be a minimum of whichever is higher of:

300millimetres (mm) above the general ground level of the site

600mm above the estimated river or sea flood level

State in your assessment all levels in relation to Ordnance Datum (also known as height above average sea level). You may be able to get this information from the Ordnance Survey. If not, you’ll need to get a land survey carried out by a qualified surveyor.

28 February 2017
Changed URL for Find out what flood zone your development is in, to the new Flood Map for Planning service.
Changed URL for Check if your development is within 20 metres (m) of a main river, to the Main River map